Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 220354

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1054 PM CDT Mon Aug 21 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 355 PM CDT Mon Aug 21 2017

Once again, we have seen widespread thunderstorm activity across IA
rob us of instability/moisture. We still expect the bulk of the
thunderstorm activity to remain in IA with the instability, but we
will see a shield of stratiform precip move from southern MN toward
western WI in a zone of moist lift within the right entrance region
of an upper jet that extends from central MN over into eastern
Ontario. Once this shield of rain moves through, that`s it for rain
locally, likely until the weekend.

The biggest issue we have had with the rain is the bit of a wake low
that has developed. On the back edge of the rain, we have see a good
30 minutes or so where winds have gusted to between 30 and 40 mph.
Pressures with the low don`t look extreme enough though to lead to
winds getting much stronger than what we are seeing now.

For tonight, clouds will clear out from west to east, with northwest
winds remaining in the 5-10 mph range. These winds will keep us from
seeing fog and usher in dewpoints into the 50s. If you are wondering
what Tuesday`s weather will be like, look up in North Dakota today.
Highs in the mid 70s with dewpoints mixing down into the mid 40s to
mid 50s with northwest winds gusting to between 25 and 30 mph.

.LONG TERM...(Tuesday night through Monday)
Issued at 355 PM CDT Mon Aug 21 2017

The best chance for precip appears to be next weekend. Meanwhile
expect cool and dry weather on Wednesday, with a gradual warm up
over the latter half of the week.

Northwest flow will be in place across the region Tuesday night,
with subsidence and surface high pressure centered across the Upper
Mississippi River Valley. This will set the stage for a dry and
sunny day on Wednesday with light and variable winds and dewpoints
in the 50s. An upper level short wave will swing through the region
late Wednesday, and the GFS/GEM/NAM all produce some light QPF north
of I-94, but the ECMWF is dry. Forecast soundings are quite
saturated ahead of this wave, so a slight chance of pops is
justified during this time period.

Looking ahead, a strong upper level trough will move onshore the
Pacific northwest on Thursday with lee side troughing over the High
Plains. Southerly flow will develop across the Midwest as the
surface high tracks eastward toward the Great Lakes. This will bring
a return of slightly warmer air along with more moisture by Friday
and Saturday as dewpoints climb back into the lower 60s. Saturated
mid levels will keep the instability potential at bay, but should
see a few hundred J/kg of MUCAPE Saturday afternoon along with PWAT
values near 1.5". This is not a concerning environment in terms of
severe weather or heavy rain, but it does support widespread showers
and thunderstorms for the weekend.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1050 PM CDT Mon Aug 21 2017

Clearing skies continue working across the area tonight. Wind
should be enough to suppress widespread fog formation, and dry
northwesterly flow. VFR will continue through the period with the
main focus tomorrow being the gusty northwest winds. Generally
expect about 15G25kts at most locations by mid afternoon.
Decoupling near sunset and falling AOB 7 knots tomorrow evening.

KMSP...No change from the main discussion.

WED...VFR. Wind N 5 kts.
THU...VFR. Wind SE 5 kts.
FRI...VFR. Wind SE 5-10 kts.




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